Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.29   10.461%   $266.5313   $266.53   $266.55   $266.50  
  Purchase #2 $92.27   5.671%   $97.5026   $97.50   $97.50   $97.50  
  Purchase #3 $232.74   10.407%   $256.9613   $256.96   $256.95   $257.00  
  Purchase #4 $239.64   9.567%   $262.5664   $262.57   $262.55   $262.60  
  Purchase #5 $46.29   6.824%   $49.4488   $49.45   $49.45   $49.40  
  Purchase #6 $48.95   11.682%   $54.6683   $54.67   $54.65   $54.70  
  Purchase #7 $116.37   6.850%   $124.3413   $124.34   $124.35   $124.30  
  7 purchase totals = $1,017.55       $1,112.0200   $1,112.02   $1,112.00   $1,112.00